How to Access the Last Element of a Go Slice in Templates?

Accessing the Last Element of a Slice in Go Templates

Retrieving the last element of a slice within a Go template can be challenging due to the zero-based indexing used in templates. While it's straightforward to obtain the slice size and index individual elements, referencing the last element using the size alone leads to an "out of range" error.

Using FuncMaps for Arithmetic Operations

To overcome this limitation without resorting to custom function definitions, one can leverage FuncMaps to introduce custom functions into the template rendering process. For instance, an "add" function can be defined as follows:

t := template.Must(template.New("").Funcs(template.FuncMap{
    "add": func(a, b int) int { return a + b },
}).Parse(theTemplate)

Employing the Custom Function

With the "add" function available in the FuncMap, you can access the last element of the slice like this:

{{index .Things (add $size -1)}}

This expression effectively subtracts one from the slice size, allowing you to index the last element without triggering an out-of-range error.

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